docs: def _where(filename, dirs=[], env="PATH"):
      """Find file in current dir or system path"""
      if not isinstance(dirs, list):
          dirs = [dirs]
      if glob(filename):
          return filename
      paths = [os.curdir] + os.environ[env].split(os.path.pathsep) + dirs
      for path in paths:
          for match in glob(os.path.join(path, filename)):
              if match:
                  return os.path.normpath(match)
      raise IOError("File not found: %s" % filename)